1. Field of the Invention
The present invention relates to an uneven-pattern reading apparatus for reading an uneven surface pattern such as a fingerprint used for identifying an individual.
2. Description of the Related Art
FIG. 15 is a schematic diagram of a conventional uneven-pattern reading apparatus, which is disclosed in, for instance, Japanese Patent Unexamined Publication No. 13446/1980. Reference character L denotes an incident light beam from a light source. Numeral 4 denotes a detecting prism which is a base for placing a finger for detecting a fingerprint. Numeral 5 denotes a fingertip. Numeral 5a denotes an uneven pattern such as a fingerprint. Numeral 7 denotes an imaging device for imaging the pattern of the fingerprint formed by a light beam which is emitted from the illuminating light and reflected from the finger. Numeral 8 denotes a processing device for processing the picked up image. Numeral 20 denotes an image-forming lens for forming an image of the pattern of the fingerprint on the imaging device. Numeral 21 denotes a television camera which is the imaging device. Numeral 41 denotes an incident surface of the detecting prism 4 upon which the light beam is made incident; 42 denotes a detecting surface of the detecting prism 4; and 43 denotes an emergent surface of the detecting prism 4 from which the reflected light beam is made emergent. Reference character L denotes the light beam.
Next, a description will be given of the operation. The fingertip 5 of a subject is brought into close contact with the detecting surface 42 of the detecting prism 4, and an incident light beam 1 incident upon the incident surface 41 of the detecting prism 4 is illuminated to the fingertip 5.
Here, if it is assumed that, at the detecting surface 42, the angle of incidence "THgr"i of the light beam L is greater than or equal to a critical angle "THgr"c with respect to an air layer, at the portion where the projecting surface of the fingerprint is in close contact, the light is transmitted through the interior of the finger, the amount of the reflected light beam from the detecting surface 42 is small. On the other hand, if there is an air layer formed by the detecting surface 42 and the projecting surface portions of the fingerprint at the finger tip 5, the incident light beam is totally reflected from the detecting surface 42.
Pattern information of the fingerprint, which is this reflected light beam, is outputted from the emergent surface 43 of the detecting prism 4. An image of this reflected light beam is formed on the imaging surface of the television camera 21 of the imaging device 7 to image the pattern of the fingerprint, and this pattern information is processed by the processing device 8, thereby making it possible to identify the fingerprint.
Since the conventional uneven-pattern reading apparatus is arranged such that the imaging surface of the imaging device 7 constitutes an imaging surface of the image-forming lens 20 with respect to the pattern of the subject, there has been a problem in that an optical path length of a predetermined length is required, making the apparatus large. In addition, there has been a problem, among others, in that if an attempt is made to make the apparatus compact by shortening the focal length, the pattern information becomes distorted, or a bright light source is required.
The present invention has been devised, and its object is to obtain a compact, lightweight uneven-pattern reading apparatus in which the optical path length from the detecting surface to the imaging surface is short.
An uneven-pattern reading apparatus in accordance with a first aspect of the present invention comprises: a detecting prism having a detecting surface on which an uneven pattern is placed, an incident surface upon which an incident light beam for illuminating the uneven pattern is incident, and an emergent surface from which a reflected light beam of the uneven pattern from the detecting surface is emergent, angles between the respective surfaces being provided such that the incident light beam is applied to the uneven pattern and the reflected light beam from the detecting surface is emergent from the emergent surface; incident-light-beam converging means for causing the incident light beam from a light source to be incident upon the incident surface after making the incident light beam from the light source parallel or convergent with respect to an optical axis of the incident light beam; an imaging device for picking up the reflected image emergent from the detecting prism; a converging optical system for converging the emergent light beam emergent from the emergent surface upon an imaging surface of the imaging device after making the emergent light beam emergent from the emergent surface parallel or convergent; and a processing device for identifying the uneven pattern on the basis of the image picked up by the imaging device, wherein an imaging surface of the imaging device is provided closer toward an emergent surface side than a focusing position of the converging optical system.
In an uneven-pattern reading apparatus in accordance with a second aspect of the present invention, vertical and horizontal magnifications of the incident-light-beam converging means or the emergent-light-beam converging means differ.
In an uneven-pattern reading apparatus in accordance with a third aspect of the present invention, the incident-light-beam converging means has diffusing means provided between the light source and the incident surface of the detecting prism for diffusing the light beam from the light source.
In an uneven-pattern reading apparatus in accordance with a fourth aspect of the present invention, the incident-light-beam converging means is arranged such that means for diffusing the light beam and means for making the light beam parallel or convergent are formed integrally.
In an uneven-pattern reading apparatus in accordance with a fifth aspect of the present invention, the detecting prism has means provided on the incident surface or the emergent surface for making the light beam parallel or convergent in a predetermined direction.
In an uneven-pattern reading apparatus in accordance with a sixth aspect of the present invention, the detecting prism has angles between surfaces for making the incident light beam and the emergent light beam parallel to the detecting surface.
In an uneven-pattern reading apparatus in accordance with a seventh aspect of the present invention, means for making the incident light beam upon the incident surface of the detecting prism has returning means for returning the light beam, the returning means being provided between the light source and the incident surface of the detecting prism or between the detecting surface and the imaging surface of the imaging device.